CCE Substructure for Ceramics 2 — Questions and Answers
Question 1: Which metal alloy type offers the highest bond strength with ceramic veneers due to its oxide layer formation?
- High-gold alloy
- Base metal alloy (Correct answer)
- Palladium-silver alloy
- Titanium alloy
Correct answer: Base metal alloy
Base metal alloys form a robust oxide layer that chemically bonds to dental porcelain, providing superior ceramic adhesion.
Question 2: When designing a metal substructure, the recommended minimum metal thickness for strength without excess bulk is:
- 0.1–0.2 mm
- 0.3–0.5 mm (Correct answer)
- 0.7–1.0 mm
- 1.5–2.0 mm
Correct answer: 0.3–0.5 mm
A metal coping thickness of 0.3–0.5 mm provides adequate rigidity to support the overlying ceramic without adding unnecessary bulk.
Question 3: What purpose does the oxidation (degassing) firing serve in preparing a metal substructure for porcelain?
- It increases metal hardness
- It removes surface contaminants and forms an oxide layer (Correct answer)
- It expands the metal to match ceramic CTE
- It creates a matte finish for esthetics
Correct answer: It removes surface contaminants and forms an oxide layer
Oxidation firing burns off organic contaminants and creates a controlled oxide layer that promotes chemical bonding with the opaque porcelain.
Question 4: A connector on a fixed partial denture (FPD) substructure must have a minimum cross-sectional area of approximately:
- 1 mm²
- 2 mm²
- 4 mm² (Correct answer)
- 8 mm²
Correct answer: 4 mm²
A minimum 4 mm² cross-sectional area for connectors is recommended to resist fracture under functional occlusal loading.
Question 5: Which design feature of a porcelain-fused-to-metal (PFM) coping helps prevent porcelain fracture at the facial margin?
- Sharp 90-degree shoulder
- Metal collar or labial shoulder chamfer (Correct answer)
- Feather-edge finish line
- Open margin design
Correct answer: Metal collar or labial shoulder chamfer
A metal collar or deep chamfer at the facial margin supports the porcelain edge and prevents chipping by eliminating unsupported ceramic.
Question 6: Which property is most critical when matching a metal alloy to a specific dental ceramic for a PFM restoration?
- Vickers hardness
- Coefficient of thermal expansion (CTE) (Correct answer)
- Ultimate tensile strength
- Proportional limit
Correct answer: Coefficient of thermal expansion (CTE)
The CTE of the metal and ceramic must be closely matched (metal slightly higher) to prevent residual stress and ceramic fracture during cooling.
Question 7: What is the primary advantage of a zirconia substructure over a metal substructure for all-ceramic restorations?
- Lower cost of fabrication
- Elimination of a metal-ceramic interface and improved esthetics (Correct answer)
- Higher thermal conductivity
- Easier occlusal adjustment
Correct answer: Elimination of a metal-ceramic interface and improved esthetics
Zirconia substructures eliminate the opaque metal coping, allowing superior light transmission and a more natural tooth appearance.
CCE Substructure for Ceramics 2
Which metal alloy type offers the highest bond strength with ceramic veneers due to its oxide layer formation?